A 73-year-old man has been accused of sexually abusing five girls when he was babysitting in Perth's south between 2002 and 2005.

Police say the crimes were committed in the Warnbro area and involved girls aged between six and 11 at the time of the first incident.

The man has been charged with 31 offences including 14 counts of sexual penetration of a child under 13 years, and is due to face Rockingham Magistrates Court on May 6.

Police say the investigation is ongoing and urge anyone with information about the case to make contact.

AAP